Bosch Extra Length Aircraft Black Oxide Drill Bit

Why I reached for this long-reach bit

There are jobs where a standard twist bit simply can’t get there—think drilling through a cabinet face while clearing a protruding frame, or popping a pilot through a bracket tucked behind a crossmember. I picked up Bosch’s long-reach bit specifically for these awkward scenarios, and it’s become the one I keep in the side pocket of my drill bag for problem-solving. It’s a straightforward tool—black oxide high-speed steel with a speed-helix twist—but the combination of length options and consistent chip evacuation makes it more versatile than it first appears.

Design and build

The bit is a classic twist pattern with a speed-helix geometry that moves chips efficiently. The black oxide finish gives it a slick surface and some corrosion resistance without the brittleness you sometimes get from harder coatings. It’s available in two overall lengths: 6 inches with a 4-inch working length, and 12 inches with a 10-inch working length. That extra reach is the whole point, and it’s generous enough to actually matter in the field.

Sizes range from 1/16 inch through 3/8 inch in the 6-inch length, and from 1/16 inch up to 1/2 inch in the 12-inch length. Each size is sold individually. I primarily used the 1/8, 1/4, and 3/16 in both lengths, with occasional use of the 3/8 for larger clearance holes.

Fit and finish are solid. Shanks are straight, the flutes are cleanly ground, and the black oxide is uniform. I didn’t notice any obvious runout in the samples I tested when chucked in a quality cordless drill and a benchtop press.

Performance across materials

I tested the bit in common shop materials—softwoods, hardwoods, plastics, and mild steel—focusing on how the speed-helix clears chips in deeper holes and how the extra length affects control.

• Wood (softwood and maple): Clean entry and predictable chip ejection. The long reach was especially handy for drilling through assembled casework where there was no line-of-sight for a shorter bit. With the 1/4-inch size, I was able to drill a full 4-inch-deep pilot through a face frame without burning. The speed-helix helps keep the flutes from packing.

• Plastics (acrylic and ABS): No melting with moderate RPM and light feed. The longer bit adds leverage, so it wants to pull if you’re too aggressive on breakthrough—backing off in the last eighth of an inch avoids chipping on the exit.

• Mild steel (mending plates and 1/8-inch tubing): With a couple drops of oil and a sensible feed rate, the bit cut smoothly. The speed-helix geometry shed chips well, which matters with the longer working lengths; it reduces the urge to “peck” constantly. For deeper holes in tubing, I still used a short pilot first to keep alignment dead-on, then followed with the long bit to finish depth.

I wouldn’t choose a black oxide HSS bit for stainless, hardened fasteners, or repeated heavy-duty drilling in thick steel—cobalt or carbide is the safer play there—but for general fabrication, brackets, enclosures, and automotive sheetmetal, the Bosch long bit holds its own.

Reach and control

Extra length brings advantages and quirks. The obvious win is access: the 6-inch bit’s 4-inch working length will sneak past protrusions, and the 12-inch option genuinely opens up jobs like drilling through deep jambs or reaching across a cavity without dismantling half the assembly. I used the 12-inch 1/8-inch bit to drill pilot holes through a pair of stacked 2x members while clearing a pipe, and the 10-inch working length made it a non-event.

The tradeoff is flex. Long bits will deflect under side load, and small diameters like 1/16 and 3/32 require a patient hand. A few technique adjustments help:
- Start holes with a punch or a shorter bit for accuracy, then switch to the long bit once the path is established.
- Reduce RPM as diameter increases, especially in metal. Keep pressure steady to avoid bowing the bit.
- Support the drill close to the work when possible; a guide block or bushing works wonders for straightness on deep bores.

Used this way, I had no issues with chatter beyond what’s typical for long tooling.

Chip evacuation and the speed-helix

The speed-helix geometry is the quiet hero here. In deeper holes, chips can compact and overheat a conventional flute. With this bit, I noticed fewer stalls and less need to peck constantly, particularly in wood and aluminum. In mild steel, I still pecked intermittently to keep temperatures in check, but chip evacuation was more efficient than with a standard helix. That shows up most with the 12-inch sizes, where you’re moving material a long way up the flutes.

Durability and maintenance

The black oxide finish reduces friction and offers light corrosion protection. Over several sessions, the coating wore as expected at the cutting edges and along the primary flute surfaces, which is normal. Edge retention was better than generic big-box long bits I’ve used, particularly in the smaller diameters. After a fair amount of use in wood and mild steel, the 1/4-inch bit still cut cleanly, though I could feel a slight increase in feed pressure compared with new. High-speed steel is resharpenable, and the geometry here takes a touch-up well if you’re comfortable at the grinder.

What I didn’t see: galling in the flutes, flaking, or sudden dulling. What you should still avoid: dry drilling thick steel at high speed, and forcing the bit to act like a pry bar—long bits don’t forgive side loading.

Practical tips for best results

• Use a pilot hole or a centering punch to minimize wander, especially on metal and glossy plastics.
• Manage heat: drop the RPM and use oil for steel, clear chips regularly on deep holes.
• Support alignment with a guide block or bushing when accuracy matters over long depths.
• For the smallest diameters, let the bit cut at its pace. If you bow it, it will snap.
• Expect a single bit per package—order multiples for the sizes you burn through most.

Where this bit earns its keep

If you work in cabinetry, electrical, HVAC, auto/moto, or light fabrication, you know the value of reach. I used the Bosch long bit for:
- Drilling pilots for cabinet pulls over wide stiles without removing doors.
- Running holes through nested framing members with obstructions in the way.
- Reaching past a steering rack mount to drill a bracket without disassembly.
- Adding hardware inside deep boxes where a normal bit can’t clear the edge.

It’s a convenience tool that also performs like a daily driver for general drilling.

What I’d change

• A split-point option would help reduce walking on metal, especially for field work without a punch. As is, technique covers it, but it would be welcome.
• A multi-bit pack for common sizes could cut down on reordering and keep spares on hand.
• A sleeve or simple alignment guide bundled with the 12-inch sizes would help users new to long bits maintain straightness on deep bores.

None of these are deal-breakers, but they’d make a good tool even more user-friendly.

Final recommendation

I recommend the Bosch long-reach bit for anyone who needs reliable extra length with predictable cutting behavior. The speed-helix geometry moves chips efficiently, the black oxide finish holds up as expected, and the mix of 6-inch and 12-inch options—with 4-inch and 10-inch working lengths—covers most access challenges I run into on site and in the shop. It’s not the right choice for stainless or hardened steel, and the inherent flexibility of long bits demands sound technique, but within its lane it’s a dependable, well-executed solution that earns a permanent spot in the kit.